Internal combustion engines may be used to provide motive power to a vehicle. During operation of an engine exhaust gases are removed from one or more cylinders after combustion. Subsequently fresh air and gas are flowed into the one or more cylinders for another combustion cycle.
Intake and exhaust ports may be included in the cylinder and provide fluidic communication between the intake and exhaust systems and the cylinder. Thus, the intake port provides intake air to the cylinder and the exhaust port enables exhaust gases to be expelled from the cylinder. It will be appreciated that the intake and exhaust ports may be referred to as ports.
To control combustion, lift-valves (e.g., intake valve, exhaust valve) may be used to provide an oscillatory lifting movement and in this way open and close the intake and exhaust ports. It will be appreciated that the engine may perform a four-stroke combustion cycle. Furthermore, valve actuating mechanisms are used to adjust or move the lift-valves. The valves and valve actuating mechanism may be referred to as a valve train. The valve train functions to open and close the intake and exhaust ports at desired time intervals. One of the objectives of the valve train may be to open the intake and exhaust ports quickly to reduce throttles losses in the intake and exhaust gas flows to provide efficient charging of the cylinder with intake air and completely expel exhaust gasses from the cylinder. Some engines are equipped with two or more intake and exhaust ports. Tappets may be included in the valve actuating mechanisms. In some engines, electrically controlled solenoid valves are used to connect the tappets to the oil circuit or to isolate the tappets from the oil circuit. In this way, valve operation may be enabled or inhibited via the electronically controlled solenoid valves. Specifically, an electromagnet, which when energized opens the solenoid valve, is activated by an engine control.
The Inventors have recognized several drawbacks with using electronically controlled solenoid valves to adjust the tappets. Firstly, electronically controlled solenoid valves may be expensive and therefore increase the engine's cost. The high costs of these electrically controlled and actuated valves represent an obstacle to their use in large scale production. Furthermore, the complex design of the solenoid valves may be prone to failure and/or malfunctioning. A further disadvantage lies in the complex control of the valve and in the event of solenoid valve failure or malfunction the valve may fail to open.
As such in one approach, a method for operating an engine is provided. The method comprises adjusting an oil pressure in an oil circuit, the oil circuit including a pump in fluidic communication with a hydraulically adjustable cam follower and switching the hydraulically adjustable cam follower into a connected state to a disconnected in response to the oil pressure adjustment.
In this way, the state of the hydraulically adjustable cam follower may be switched based on the oil pressure in the oil circuit. Thus, the cam follower can be passively switched via internal components in the cam follower. As a result, the cost of the engine is reduced when compared to engines that may utilize solenoid valves to control cam followers. Moreover, the likelihood of cam follower malfunctioning may be decreased when the cam followers are passively switched.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
The Invention is described in more detail below with reference to FIGS. 1-4.